RT Journal Article
T1 The phenomenon of deficient electron microprobe totalsin radiation-damaged and altered zircon
A1 Nasdala, Lutz
A1 Kronz, Andreas
A1 Wirth, Richard
A1 Váczi, Tamas
A1 Pérez-Soba Aguilar, Cecilia María
A1 Willner, Arné
A1 Kennedy, Allen K.
AB The phenomenon of deficient electron microprobe analyses, with sums of analyzed constituents often below 95 wt%, isassigned to the analysis of altered, porous minerals. With the example of three zircon populations we show that low totalsare related to textural features (i.e., numerous pores of tens to hundreds of nanometers size) as well as to the chemical composition(i.e., water content well within the wt% range, which may affect partial sample degradation under the electron beam).The formation of the spongy texture is explained by the alteration of a previously radiation-damaged and, thus, volumeexpandedmaterial in a fluid-driven replacement reaction. The smaller volume of the reaction product (crystalline, non volume-expanded zircon) accounts for the formation of numerous voids and pores, which are perfect candidates for the incorporationof water. The alteration has also resulted in uptake of non-formula elements such as Al, P, Ca, Fe, Y, and REEswhereas Si and Zr are depleted. In one case, strong uptake of non-radiogenic Pb in altered zircon was observed. Because porous,low-total zircon has formed in secondary alteration process, its occurrence can be considered as an indicator of a secondaryalteration history of the host rock. Low-total zircon is easily recognized by very low electron back-scatterintensities, which are closely related to the two main causes of the analytical shortfall (i.e., water content and porosity)and often lowered furthermore by the presence of light non-formula elements (especially P and Fe) up to the wt% range.
PB Elsevier Science Ltd
SN 0016-7037
YR 2009
FD 2009
LK https://hdl.handle.net/20.500.14352/50204
UL https://hdl.handle.net/20.500.14352/50204
LA eng
DS Docta Complutense
RD 3 abr 2025